GADOLINIUM-DTPA AND GADODIAMIDE AS AN ALT ERNATIVE CONTRAST-MEDIUM FOR CT

Purpose: To evaluate the effect of intravenously applied gadolinium-ba sed contrast medium in computed tomographic (CT) studies. Material and methods: Serial dilutions of iohexol 300, Gd-DTPA and gadodiamide wer e scanned with CT in a phantom study using water filled tubes. For qua ntification of x-ray attenuation, the mean Hounsfield units (HU) were calculated from the CT scans. Five patients with contraindications aga inst iodine contrast agents were examined with abdominal or thoracic C T before and after application of 0.2 mmol/kg body weight of a gadolin ium-based contrast agent. In these patients attenuation values were ob tained in ROI from unenhanced and enhanced CT scans. Results: The phan tom study revealed a 38.4% enhancement for Gd-DTPA and a 35.7% enhance ment for gadodiamide scaled on the reference measurements with iohexol 300. Thus, 130.2 ml Gd-DTPA or 140.1 ml gadodiamide are needed to ach ieve the same attenuation as an i.v. injection of 50 ml iohexol 300. C onsequently the corresponding dose of 1 mmol/kg body weight would exce ed the manufacturer's recommended dose. In four patients with complete thoracic or abdominal CT, i.v. applied gadolinium-based contrast medi um (0.2 mmol/kg) yielded no visible advantage. In these patients paren chymal enhancement did not exceed 25%. Dynamic CT of a patient with fo cal liver lesion revealed an arterial enhancement peak of 75%. Conclus ion: Sufficient parenchymal enhancement in CT studies cannot be achiev ed with the available gadolinium-based contrast mediums. They might be helpful if only short time vascular enhancement is required.